A prior art method of transmitting graphic images is generally known by the name “teletext”. The World System Teletext standard has been adopted in many countries for the simultaneous transmission of textual and graphic information with a conventional analog television signal. The teletext system is particularly used for the transmission of subtitles associated with a television program.
Meanwhile, the MPEG2 (ISO/IEC 13818) digital television standard will be applied worldwide for the broadcast of digital television programs to the end-user by satellite, cable, terrestrial networks, and by packaged media such as tape or disc. A multitude of integrated circuits for MPEG2 decompression and demultiplexing are on the market and will be applied in receiver decoders for the purpose of receiving and decoding of broadcast television programs or decoding of packaged (multi-)media.
The MPEG2 compression and multiplexing technology will provide the end-user a very large choice in programs (typically in the order of hundreds), which will require an easy-to-use “man-machine interface”. It is expected that the end-user will associate “digital” with high quality. High quality must therefore be manifest in all aspects of the service that will be provided. Typical of satellite broadcast is the large footprint of its reception area, which usually encompasses multiple language areas. Many of the television programs to be broadcast will therefore also be targeted at multiple language areas, which requires multi-language subtitling capabilities. The attractiveness and readability of subtitles will have a major impact on the end-user's willingness to watch a television program in a language spoken other than his or her own.
The prior art teletext system is very limited in quality and performance. It is a character-based transmission system, in which coded data is transmitted to define which characters are to be displayed. The appearance of the subtitles (in terms of character font, spacing, graphic capabilities, colours) is fixed in hardware. Further, the present teletext system is not able to support complex character sets such as used in the People's Republic of China and Japan. The character-based system would require very expensive and complex character generators in case of supporting multiple character sets, or in case of a single but very complex character set. The prior art teletext system thus provides only a basic solution for multi-language subtitling.